Hugoniot sound velocities and phase transformations in two silicates

Abstract

Rarefaction wave velocities have been used to estimate sound velocities on the Hugoniot for a quartz rock and for a perthitic feldspar. The Hugoniot states and rarefaction wave velocities were determined with multiple manganin stress gages placed between successive slabs of the sample material. Hugoniot stress states were produced by impact from explosively driven flyer plates. The sound velocity was determined from the transit time across gage planes of the initial characteristic of the rarefaction wave originating at the flyer plate free surface. Sound velocities (referred to Eulerian coordinates) measured in quartzite were 7.6, 8.1, and 10.5 mm/μS at Hugoniot stresses of 220, 250, and 355 kbar, respectively. Sound velocities measured in feldspar were 7.4, 8.7, and 9.2 mm/μs at Hugoniot stresses of 255, 345, and 460 kbar, respectively. These velocities are close to estimated bulk velocities and imply an almost complete loss of material strength behind the shock front. On the basis of our measured sound velocities and earlier observations by others we suggest that the Hugoniot yielding phenomenon is an adiabatic shear process resulting in partial melting behind the shock front. We further suggest that inhomogeneity in the adiabatic shear process may account for many details of the nonequilibrium mixed phase Hugoniot observed in silicates.

Dynamic properties of ceramic materials

“…The existence of metastable mixed-phase Hugoniot states over a broad stress range in quartz was inferred from the interpretation of earlier shock data. A theory of microstructural deformation and thermal heterogeneity was proposed (Grady, et a/., 1975; which was consistent with this metastable Hugoniot along with much of the dynamic and post-shock recovery data.…”

Estimating shock pressures based on high-pressure minerals in shock-induced melt veins of L chondrites

“…Shock-wave interactions between different shock impedance materials may cause localized melting, which is most pronounced at the interface of metal-troilite and silicates, and the interface of minerals and pore space (Kieffer 1971;Stöffler et al 1991;Schmitt 2000;Sharp and De Carli 2006). Friction by shear along the contacts of materials of vastly contrasting shock impedance and along fractures may also produce local melting (Gault et al 1968;Kieffer 1975;Grady et al 1975;Spray 1998;Kenkmann et al 2000). Adiabatic shear can produce temperatures that are thousands of degrees hotter in shear regions than in immediately adjacent material (Grady et al 1975).…”

“…Friction by shear along the contacts of materials of vastly contrasting shock impedance and along fractures may also produce local melting (Gault et al 1968;Kieffer 1975;Grady et al 1975;Spray 1998;Kenkmann et al 2000). Adiabatic shear can produce temperatures that are thousands of degrees hotter in shear regions than in immediately adjacent material (Grady et al 1975). Although adiabatic shear is often associated with the release phase of a pressure pulse (Nesterenko 2001), we will present calculations that show that relatively low pressures may also occur during the complex rise of a pressure pulse in a fractured rock.…”

Shock temperatures in silica glass: Implications for modes of shock‐induced deformation, phase transformation, and melting with pressure

“…This fluid like behavior is best observed during the release of a shock compressed quartz crystal from high pressure. Grady et al [1975] The transformation to the high pressure phase occurs within the shock front, little further transformation occurs during the remainder of the compression, (2) the release path for quartz shocked to less than 10 to 15 GPa returns to the initial density, (3) the release path of quartz shocked into the mixed-phase region (15 to 34 GPa) follows a path indicative of mixed quartz-stishovite, the ratio of stishovite increasing proportionally with pressure, and upon release to less than 8 GPa, reversion to a lower density approximately that of crystalline quartz, and (4) above 50 GPa the release path is essentially that of the highpressure phase until a released pressure of 5-8 GPa is reached, whereupon a reversion to a lower-pressure phase with a density of-•2.2 Mg/m3 occurs.…”